Electric incandescent lamp



Get. 29, 1935.

M. R. ANDREWS- ELECTRIC INCANDESCEliT LAMP wwmV/////// Filed Oct. 50, 1931 Inventor'- M ary RAndPews, y M7 Her-Attoi-ney tures or compounds.

Patented Oct. 29, 1935 UNITED STATES PATENT OFFICE Mary R. Andrews, Niskayuna, N. Y.,- assignor to General Electric Company, a corporation of New York Application October 30, 1931, Serial No. 572,113

Claims.

The present invention relates to electric incandescent lamps and in particular to lamps containing as a light source a body of a carbide of a refractory metal, such as tantalum, hafnium, zirconium, niobium, and the like, or mixtures of such carbides. While such carbides can be operated at exceedingly high temperatures because of their highly refractory nature, it has been found that a slow dissociation occurs which eventually leads to their destruction.

In accordance with my invention dissociation of carbide incandescent bodies is retarded, or prevented, by bringing carbon vapor from a source of uncombined carbon into contact with them while they are at an operating temperature. Carbon vapor may be supplied by a carbonaceous body maintained at incandescence and located at some distance from the carbide body, preferably below it. Or, carbon may be supplied by a carbonaceous member located in the immediate vicinity of the carbide body. For example, the carbon may constitute a core located in a shell of carbide.

My invention will be described in greater detail in connection with the accompanying drawing which shows in Fig. 1 a lamp having a carbide lighting body and also a second body 01 carbon from which carbon can be evaporated or sputtered; Fig. 2 shows a modification in which the carbonaceous material is contained as a core within a carbide filament; Fig. 3 shows an en-' larged cross-section of a filament such as shown in Fig. 2; Fig. 4 shows a second modification in which the carbonaceous vapor is obtained from carbonaceous electrodes between which an arc-like discharge is operated; and Figs. 5 and 6 respectively are vertical and horizontal sectional views of a press suitable for extruding composite filaments such as are employed in the lamp of Fig. 2.

In the lamp shown inFig. 1 the elongated bulb 5 of suitable transparent material such as glass having a stem 6 is provided with a filament 1, consisting of tantalum carbide, hafnium carbide, niobium carbide, zirconium carbide, or other suitable refractory carbide, or their mix- The following are examples of mixtures suitable for the purposes of my invention: (1) a mixture of four parts tantalum carbide and one part hafnium carbide; (2) a mixture of four parts tantalum carbide and one part zirconium carbide. The filament,

although shown in Fig.1 as of a. simple hairpin shape, may have various configurations well.

pasting,-or otherwise, to leading-in conductors 0,

9 which are sealed into stem 6.

The carbide filament may be made by the well.

known extrusion process, for example tantalum oxide may bevconverted with a suitable paste, 5

such as a flour or starch paste, or a suitable gum or cellulose binder, into a plastic material suitable for extrusion. The extruded filaments are baked while covered with lamp-black or other carbonaceous material in a hydrogen atmosphere m at a temperature sufliciently high to convert the oxide to the carbide. I prefer to employ for this purpose a temperature of about 1775". K. (1500 C.)

In Fig. 1 there is shown, as a source of carbon vapor a small rod'or filament III of graphite, or other suitable carbonaceous material, attached to leading-in conductors H and l2.

. The container in either modification is baked, exhausted and filled with a suitable inert gas, such for example as argon or neon, at a pressure sufiiciently high to retard thermal volatilization of the carbide filament during operation. I may employ gas pressures within the range or about one-half to two atmospheres.

The carbide filament 1 during operation or the lamp may be heated by suitable passage of current to a temperature of about 3400 to 3500 K. The carbon rod is maintained at about 2400 K. or higher. As is well known, the tem- 3 perature may be controlled by proper coordina-- tion of the voltage, the diameter and length of the carbon rod. Its temperature also depends to some extent on the temperature of the carbide filament. For example, with a 17 mil tantalum carbide filament 10.1 centimeters long operated at 300 watts per square centimeter a graphite rod about three inches long and about 44 mils in diameter when operated at 31.5 amperes supplied -more than enough carbon to .keepthe carbide filament carbidized to the carbide containing the higher amount of carbon, but when run at about 29 amperes did not supply enough to maintain the higher carbide. In practice it is necessary to supply only enough 45 carbon to maintain the filament as the carbide containing the lower amount of carbon, TaaCa, since this has a very high melting point. At such temperature the filament I 0 will have a long life but minute amounts of carbon vapor are evolved from it and are carried upward into contact with the carbide filament I by thegas convection currents in the bulb.

In Fig. 4 there are shown, as a source of carbon vapor, cooperating electrodes I3, I 4 consisting of carbon or graphite and being attached to conductors l5, l6 serving as supports as well as to conduct current.

In the case of the modification shown in Fig. 4 an arc-like discharge is operated between the electrodes l3, I4, the discharge being initiated by high frequency or any other known manner. Lighting the filament I before starting the arc renders starting easier as the gas becomes ionized by contact with the heated filament. The are is operated with a current value sufficiently high to heat the electrodes I3, M to such a temperature that. carbon is evaporated or sputtered in quantities which will maintain thefilament as carbide. The quantity necessary depends upon the construction of the filament and the temperature at which this filament is operated. For instance when a filament was operated at 300 watts per square centimeter of surface the are, operated at 12.6 amperes and 18 volts did not supply enough carbon to maintain the tantalum carbide filament as the carbide having the greatest amount of carbon so that this carbide decomposed slowly to the carbide: having less carbon. But, when the filament was operated at 250 watts per square centimeter, that is, at a lower temperature so that the tendency of the higher carbide to decompose was less, the arc, operated as above, supplied sufiicient carbon to recarbidize the carbide of low carbon content to that of higher carbon content.

As shown in Fig. 3, the carbonaceous material may be employed as a core 20 within a carbide shell 2|. The composite filament 22 (Fig. 2) is mounted attached to leading-in wires 23, 24 in a bulb 25 which contains an inert gas as above described.

While any suitable method of making a cored filament may be employed to fabricate the filament of Figs. 2 and 3, I have shown in Figs. 5 and 6 an extrusion press suitable for this purpose. The press here shown comprises a container having an outer wall 26 and an inner wall 21 connected by the ribs as shown in Fig. 6 and supported by a bed plate 28 ,held on a frame 29. The annular space between the walls 21 and 26 contains a quantity 3B of paste made of carbide (or carbide-yielding) material and a suitable binder, for example, starch paste. The space within the inner enclosure 21 contains 8.

quantity 3| of carbon paste, for example, graphite or charcoal with a binder. A plunger 32 having an annular member 33 and a central member 34 is arranged as shown to exert pressure on these extrudable pastes. As a result, a composite 5 filament 36 issues from the orifices at the bottom of the press. This filament has a shell of carbide (or carbide-yielding material) and a core of graphite, or other suitable carbonaceous material, and is after baking ready for mounting in w alamp.

What I claim as new and desire to secure by letters Patent of the United States is:

1. A lamp comprising a bulb, a lighting body therein consisting essentially of carbideof the 15 group of metals consisting of tantalum, hafnium, zirconium, and niobium, a separate body of carbon located adjacent to but spaced out of direct contact with said lighting body, and means for heating said carbon body. 20

2. A lamp comprising a bulb, a filament therein for giving light when at incandescence and consisting essentially of a mixture of carbides of metal including tantalum, hafnium, niobium and zirconium, a second filament of carbon spaced 25 apart from said carbide filament and terminal conductors for said carbon filament.

3. An incandescent lamp containing an incandescible body comprising a member consisting of tantalum carbide, and a source of uncombined 30 carbon for recarbidizing said member during operation of said lamp.

4. An electric lamp comprising a container, a lighting filament therein consisting essentially of tantalum carbide, a carbonaceous body 10- 5 cated adjacent to be out of direct contact with said lighting filament, and separate means for heating said carbonaceous body to supply carbon therefrom to said filament.

5. An electric lamp comprising a container, a 40 lighting body therein consisting essentially of carbide of the group of metals consisting oi. tantalum, hafnium, zirconium, and niobium, and a source of uncombined carbon in said container adapted to be heated during operation of said lamp for supplying suilicient carbon to said carbide to counteract dissociation thereof at a temperature of bright incandescence.

MARY R. ANDREWS. 

